Electron discharge device



April 14, l942 J. w. MCRAE 2,279,835

ELECTRON DISCHARGE DEVIQE Filed Dec. 21, 1940 2 Sheets-Sheet l JNVENTOR BV 1. wf; MMA@ emma Patented Apr. 14, 1942 v 2,279,835 YELrzc'rnoN DISCHARGE mavzicr.-

James W. McRae, Neptune, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 21, 1940, serial No. 371,124 6 claims. (c1. 25o-175) This invention relates to electron discharge devices and more particularly to such devices `generally denoted as electron multipliers and including a plurality of secondary electron emissive electrodes.

A general object of this invention is to improve the Vconstruction and operating characteristics of electron multipliers. More specifically, objects of this invention are:

To increase the power capacity of multistage electron multipliers;

To obtain a high degree of shielding between the input elements and the secondary electron emitters in multistage electron multipliers whereby such multipliers are adapted for eicient operation as radio frequency ampliiiers;

To simplify the construction of multielement multipliers whereby a number of the electrodes may be fabricated in a rigid, compact unitary assembly; and

To obtain a high degree of concentration-of the electrons emanating from the primary electron source in electron multipliers and acceleration of these electrons toward and focussing thereof upon the rst secondary electron emissive electrode.

In one embodiment, illustrative of this invention, an electron multiplier comprises a primary v cathode, a cylindrical collector electrode or anode coaxial with the primary cathode and a pair of groups of annular secondary electron emissive electrodes coaxial with one another and with the primary cathode. A control and an accelerating electrode or grid may be provided in cooperative relation with the primary cathode.

In accordance with one feature of this invention, the two groups of secondary cathodes are supported upon two plates, preferably of metal, lthe two plates being xedly mounted in spaced relation and supporting also the primary cathode and the grids in cooperative relation therewith, whereby a compact unitary assembly is provided. The plates overlie the secondary cathodes and form electrostatic shields which screen the discharge paths between the secondary cathodes from extraneous iields so that distortion of the elds in these paths is prevented. In addition, the plates, being closely coupled thermally to-the secondary cathodes, serve as heat radiating members whereby undue heating of the secondary cathodes, and particularly of the cathodes inthe later stages of the device, is avoided.

In accordance with another feature of this invention, shields of novel construction are provided in cooperation with the input elements of LJNifrrzi)`STATESv PATENT OFFICE ad fully from the following detailed description with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of an electron multiplier constructed in accordance with this invention, portions of the enclosing vessel and of the collector electrode or anode being broken away to show the internal structure more clearly;

Fig. 2 is a view in section of the unitary electrode assembly in Fig. l; A

Fig. 3 is an end View along plane 3-3 of Fig. 2; Fig. 4 is a view along plane 4 4 of Fig. 2, showing the coniiguration and relation of a number of the electrodes; Vand Fig. 5 is an enlarged detail view in section showincluded in the multiplier shown ing clearly the association of the supporting plates or shields. i.

Referring now to the drawings, the electron discharge deviceillustrated therein comprises a,

highly evacuated enclosing vessel Ill, of vitreous material, having at one end thereof an inwardly extending tubular portion II to which a cupshaped metallic stem I2 is hermetically sealed, the stem I2 having thereon metallic eyelets I3 to which'leading-in conductors I4 are sealed hermetically by insulating, for example glass, beads I5. Encompassing and suitably aixed to the stem I2 is a collar I6 carrying a plurality of rigid vmetallic supports or uprights I'I which in turn mount a unitary electrode assembly.

The unitary lelectrode assembly, as shown clearly in Fig. 2, comprises a pair of metallic annular iianged plates I8 and I9, which are xed in generally parallel relation by a plurality, for example three, of spacing bolts 20, as shown clearly in Fig. 5, and are connected electrically by these bolts. The plate I8 has securely iixed thereto a plurality of sleeve or coupler members 2| in which the supports vor uprights II are secured, as by welding.

Mounted in coaxial relation and supported by the plates I8 and I9 are a primary cathode, a control grid 22 andan accelerating grid 23. The cathode, as shown in Fig, 2, may be of the equipotential indirectly heated type and compriseV a cylindrical metallic sleeve 24, a restricted portion of which is provided with a coating 25 of electron emissive material. The control grid 22 and accelerating grid 23 may be helices secured to vertical wires or supports 26 `and 21, respectively. y

til

forming electrodes 29 and 30 supported on and insulated from the plates I8 and I9, respectively, The electrode 29 has a concave surface of revolution 3l and is affixed to the plate I8 by a plurality of bolts 32 the shanks of which are tightly fitted in taps in the electrode 29. The bolts 32A and the electrode 29, as shown clearly in Fig. 2, are insulated from the plate I8 by insulating washers 33. The electrode 38 is `similarly mounted on and insulated from the plate, I9 by bolts 34 and insulating washers 35, and has a convex surface of revolution 35 concentric with the surface 3l and defining therewith a dished annular passageway 31.- lA cylindrical sleeve 38 is tted within the central V,aperture on -the elec-v trode 30, is locked therein by a plug 39 and clamps the insulating disc 28 against a lip on the electrode 30 as shown.

Mounted upon and insulated from the plate I9 is a group of annular electrodes 49, 4I and 42,A

coaxial with each other and with the' cathode,

each of the electrodes 49, 4Iand 4 2 havinga dished surface A coated with a material having good secondary electron emissive characteristics. A` second group of aimular electrodes 43, 44 and 45, coaxial with one anotherand with the cathode and in staggered relation with the electrodes of the rst-mentioned group, is mounted uponv` and insulated from the plate I8, the electrodes 43 and 44 having dished surfaces A coated with a material having good secondary electron emissive characteristics and the electrode 45 having an inclined surface B similarlyy coated.

Each of the secondary electron emissive electrodes to 45, inclusive, is securely ixed to the plate I8 or I9- on which it is supported .and is also iixed securely to the adjacent electrode or electrodes of the same group. For example, the electrode 40 is secured to the plate I9 by a plurality of bolts 4G having shanks iitted in taps in the electrode 40, the electrode 48 and bolts 46 being insulated from the plate I9 by insulating members 41. The electrode 40 is also fixed rigidly with respect to the electrodel 4I. Specifically, the electrode 4I is providedV with an inwardly extending fiange 48 which is secured to the electrode 40 by a plurality,for example three, of bolts 49 and insulated therefrom by insulating members 59, the bolts extending into oversize apertures in -the plate I9. Similarly, as shown in Fig. 2, each of the other secondary electron emissive electrodes is secured to and insulated from both theplate I8 or I9 on .which it is supported and the next adjacent electrodeor electrodes of the same group. This construction, it

will be appreciated, enables the assembly of each group of electrodes as a unit with the electrodes fixed in the desired space relation, prior to the mounting of the electrodes uponthe platesY I8 and I9 and also enables the attainment of relatively small potentials across the various insulating members.

Electrical connection may be established individually to the various secondary electron emissive electrodes by leading-in conductors 5I which are sealed in the base end of the vessel I9 and each of which is connected to a corresponding `one of the electrodes 40 to 45. The leading-in conductors 5I for the upper electrodes extend through the electrode assembly.

'I'he electrode assembly described above is encompassed by a cylindrical 'anode 52 which is supported in coaxial relation with the electrodes of the assembly by a plurality of. rigid metallic supports or arms 53 extending from a metallic stud 54 sealed inthe vessel I9 and connected to a terminal 55. i

Mounted opposite the surface B ofthe secjondaryelectron emissive electrode 45 is an annular formed screen grid, V-shaped in section, which comprises spaced wires 55 secured to rigid support wires-or frames 51. The screenl gridis supported from the electrode 45 by a plurality of spaced tabs 58 secured tothe electrode 45 by screwsl 5,9 and insulated therefrom by insulating spacesli. Electrical connection to the screen grid may be established through one of the ccnductors` 5I secured to one of the tabs 58.

During operation of the device, the secondary electron emissive electrodes 40 to 45 are main` tained at successively higher positive potentials with respect to the cathode., That is, each secondary electron emissive electrode is maintained at a higher potential than the next succeeding electrode. For example, the first secondary electo the cathode andthe collector electrode or anode 52 may be operated at 2,000 volts. The plates I8 and I9 preferably are grounded. 'Ihe accelerating grid may be biased volts positive with respect to the-cathode.

Electrons emanating from thecatnode u, :s

are concentrated into a beam by the guiding electrodes 29 and 39 and are accelerated toward and impinge upon the surface A of the emissive electrode 49 whereby secondary electrons are emitted from this surface. These secondary electrons are `directed upon the surface A of the electrode 43. 'I'his action is repeated at each of `the other surfaces A and B and the electrons emanating from the electrode 45 iiow t'o the collector electrode or anode 52. At each of the secondary electron emissive surfaces A and B, the secondary electroncurrent therefrom is greater than the i electron currentv thereto. Hence,` an electron multiplication `occurs `at each of these surfaces whereby, ineffect, a multifold amplification of thecurrent flowing to the electrode 4l is realised.

'Ihe magnitude of the current flowing to the electrode 49 may be controlled, of course, by

dent that the plates I8 and I9 are closely couv pled thermally with the several secondary elecltron emissive electrodes and have large radiatingfsurfaces. Hence, these plates increase the rate of heat radiation from these electrodes and thereby assure the maintenance of the emissive surfaces A and B at a safe operating temperature.

It will be understood, of course, that the particular structure disclosed is but illustrative oi' this invention and that various modications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

l. An electron multiplier comprising a primary cathode, a/pair of spaced metallic plate members, a group of annular secondary electron emissive electrodes mounted on one of said plate members and coaxial with said primary cathode, a second group of annular secondary electron emissive electrodes mounted on the other of said plate members, coaxial with said cathode and facing said rst group of electrodes, and a co1- lector electrode coaxial with vsaid cathode.

2. An electron multiplier in accordance with claim 1 comprising a pair of beam forming electrodes coaxial with said cathode and carried by said plate members, said beam formingv electrodes being spaced and dening an annular discharge path between said cathode and one of said secondary electron emissive electrodes.

3. An electron multiplier unitary electrode assembly comprising apair of metallic discs, means nounting said discs in spaced coaxial relation, i primary cathode coaxial with said discs, a plurality of annular secondary electron emissive electrodes insulatingly mounted on one of said discs in concentric relation and coaxial with said cathode, and a plurality of concentric annular secondary electron emissive electrodes insulatingly mounted on the other of said discs in coa axial relation with said cathode.

4. An electron multiplier comprising an input element including a cathode and a control electrode in cooperative relation therewith, leadingin conductors connected to said cathode and control electrode, a plurality of annular secondary electron emissive electrodes coaxial with said input element, and means screening said secondary electron emissive electrodes from said input element including a shield encompassing said leading-in conductors.

5. An electron multiplier in accordance with claim 4 wherein said screening means includes also a pair of annular electrodesencompassing the end portions of said cathode. Y

6. An electron multiplier comprising an enclosing vessel having a cylindrical metallic stem, a unitary electrode assembly comprising a pair of metallic discs secured together in spaced substantially parallel relation, a group of concentric annular secondary electron emissive electrodes mounted on one of said discs and insulated therefrom, and a second group of concentric annular secondary electron emissive electrodes mounted on the other of said discs, insulated therefrom and in staggered relation with the electrodes of said i-lrst group, means supporting said unitary assembly from said stem, a collector electrode encompassing said assembly, an input element coaxial with said secondary electron emissive electrodes and including a cathode and a grid in cooperative relation therewith, said input element having portions between said discs, and leading-in conductors connected to said input element substantially enclosed by said metallic stem.

JAMES W. MCRAE. 

